Currently, there is no adequate monitor for noting the depth of unconsciousness of a patient under anesthesia. Rather, heart rate and blood pressure data along with response to surgical stimulation are used to merely infer consciousness. While heart rate and blood pressure can change, these changes are often unrelated both conceptually and empirically to changes in states of unconsciousness and responsiveness within the central nervous system which can provide a better indicator.
Most patients receive muscle relaxants during major surgery. In very special circumstances, which are not easily predicted, patients who are receiving potent muscle relaxants are at risk of remaining conscious of their surroundings during surgery even when receiving some anesthesia. The patients actually feel the pain of the operation but are unable to respond and communicate the pain to the medical team because of the muscle relaxant's effect. When this occurs it can be a horrendous experience because of the helplessness and the sometimes permanent changes it can bring about within the patient. The changes brought about in the patient are mostly because this aware state is undetected by the anesthesiologists and surgeons in the room by having been masked by the muscle relaxant. This state can and does occur with surprising frequency.
The ideal anesthetic is one in which the patient is comfortable throughout the procedure and emerges unaware of the operation procedure. Although this does happen, there has been no reliable indicator to the anesthesiologist as to when it is happening. The "art" of clinical anesthesia is certainly part of this system, but it is also unreliable as there are occasional failures.
The problem is serious enough that attempts at monitoring the level of consciousness of the patient have been made over the years. The electroencephalogram was the first logical system employed but has been found to be completely inadequate for various reasons.
Secondly, another monitor has appeared on the market called the lower esophageal contractility monitor. While enjoying certain advantages, the lower esophageal contractility monitor is being shown in the empirical literature to be inadequate as an accurate and reliable guide to the state of central nervous system activity.
Thirdly, a device using a surface electromyogram attached to the Frontalis muscle of a patient's face has had some success at measuring patient awareness. However, because this device only senses one facial muscle group, the information received is neither as accurate nor as reliable as the device of this application. Thus, the desire for advances in medical care as well as issues of litigation and medical ethics speak to a need to understand more about the central nervous system in terms of both consciousness and unconsciousness, effective responses to pain, and general assessment of "comfort".
The applicant's device provides a consciousness monitor which substantially advances the prior art in a new and useful way by analyzing the micro-expressions of the anesthetized patient. The device provides an accurate and reliable indictor of the consciousness of the patient and the adequacy of the anesthesia. It has been discovered by applicant that a patient's recovery from an operation can be correlated directly to the level of unconsciousness attributable to the anesthesia administered
The following prior art references reflect the state of the art of which applicant is aware and are included herewith to discharge applicant's acknowledged duty to disclose relevant prior art. It is stipulated, however, that none of these references teach singly nor render obvious when considered in any conceivable combination the nexus of the instant invention as disclosed in greater detail hereinafter and as particularly claimed.
UK Published Patent Application GB 2 113 846, Filed by Instumentarium Oy (Finland), inventors Rantala, B., et al., publication date Aug. 10, 1983 PA0 Ritchie, G., et al., A Microcomputer Based Controller for Neuromuscular Block During Surgery, Annals of Biomed. Eng. 13:3-15 (1985) PA0 Nielsen, T. A., et al., Effects of Dream Reflection on Waking Affect: Awareness of Feelings, Rorschach Movement, and Facial EMG, Sleep 12 (3) :277-286 (1989) PA0 Chang, T., et al., Continuous Electomyography for Monitoring Depth of Anesthesia, Anesth Analg. 67:521-5 (1988) PA0 Tammisto, T., et al., Assessment of Neuromuscular Block: Comparison of Three Clinical Methods and Evoked Electromyography, Eur. J. Anaesthesiol. 5:1-8 (1988) PA0 Edmonds, H. L., et al., Objective Assessment of Opioid Action by Facial Muscle Surface Electromyography (SEMG), Prog. Neuro-Psychopharmacol. & Biol. Psychiat. 22:727-738 (1988) PA0 Schwilden, H., Surveillance et Conduite de l'Anesthesie a l'Aide de l'EEG, des Potentiels Evoques, de l'EMG du Muscle Frontal ou du Monitorage de la Contractilite Oesophagienne, Ann. Fr. Anesth. Reanim. 8:162-166 (1989) PA0 Paloheimo, M., Assessment of Anaesthetic Adequacy With Upper Facial and Abdominal Wall EMG, Eur. J. Anaesthiol. 6:111-119 (1989) PA0 Edmonds, H. L., et al., Quantitative Surface Electomyography in Anesthesia and Critical Care, Int. J. Clin. Monitoring and Computing 3:135-145 (1986)
The Patent to Rantala teaches the use of a device for measuring the depth of anesthesia which combines a surface electromyogram attached to a facial muscle with an electroencephalogram and an electromyogram attached to a patient's hand. While this application does sense the facial muscle activity, it interprets the activity directly rather than using surface electromyogram readings to determine a facial expression corresponding to the consciousness of the patient, as does the applicant's device. Furthermore, the applicant's device uses an array of surface electromyograms providing a more accurate representation of a patient's facial expression, and hence a more accurate representation of the patient's consciousness state.
The article by Chang is of interest in that it also uses a surface electromyogram attached to a facial muscle group and electroencephalogram data during surgery. However, the method taught in this article was designed to effectively administer anesthesia and provided no method for monitoring the consciousness of the patient for patient comfort as does the invention described hereinbelow.
The article by Edmonds describes a device which attaches a surface electromyogam to a single facial muscle for the purpose of determining a patient's consciousness.
The device of this application more effectively achieves this purpose by sensing plural facial muscle groups simultaneously providing a more accurate and reliable indication of the patient's consciousness through sensing the facial expression of the patient. Furthermore, the device of this application provides a method for filtering out unwanted data from the sensors and a clearer method of consciousness display.
The remaining prior art listed above diverge more starkly from the present invention. By actually detecting the expression of the patient under anesthesia the applicant's device provides a measure of anesthesia adequacy which is not contemplated by any existing devices or methods.